Agricultural Meteorological Variables and Their Observations
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CHAPTER 2 AGRICULTURAL METEOROLOGICAL VARIABLES AND THEIR OBSERVATIONS 2.1 BASIC ASPECTS OF AGRICULTURAL observations are needed. The preparation of METEOROLOGICAL OBSERVATIONS advisories and services on farming methods, including irrigation and microclimate management Observations of the physical and biological varia- and manipulation, also requires specialized data. bles in the environment are essential in agricultural Finally, the needs of research call for detailed and meteorology. Meteorological considerations enter precise data according to each research topic. There into assessing the performance of plants and are too many specialized methods to be included in animals because their growth is a result of the this review, but almost all research projects require combined effect of genetic characteristics (nature) information on the background climatology that and their response to the environment (nurture). may be derived from the outputs of the long-term Without quantitative data, agrometeorological types of stations listed below. planning, forecasting, research and services by agrometeorologists cannot properly assist agricul- 2.1.1 Data as a support system for tural producers to survive and to meet the agrometeorological services ever-increasing demands for food and agricultural by-products. Such data are also needed to assess the In section 1.4.1 of Chapter 1, data are considered impacts of agricultural activities and processes on parts of support systems for agrometeorological the environment and climate. The following services. This applies to assessments as well as sections provide guidance on the types of observa- predictions. It should be stressed that this refers to tions required, their extent, organization and real data, that is, observed parameters, or “ground accuracy, as well as on the instruments needed to truth”. As already mentioned in Chapter 1, collec- obtain the data, with an emphasis on those for tion of good observations has gone out of fashion operational and long-term stations. Older books on in many countries because of the illusion that measurements are generally available to the public, computer-modelled estimates can replace them. but more recently, the number of books with Models can be useful only if they get real input data components useful to agricultural meteorology has and if additional real observations are available to diminished. Reference can be made here, for exam- check the validity of model output. ple, to books that have become more widely used since the previous edition of this Guide was When the data are to be related to agricultural oper- compiled, such as Fritschen and Gay (1979), ations, agricultural data are also essential, including Greacen (1981), Meteorological Office (1981), the state of the crops and of animals. These comple- Woodward and Sheehy (1983), Russell et al. (1989), mentary data are often collected by Pearcy et al. (1989), Goel and Norman (1990), non-meteorological personnel. For all agrometeor- Kaimal and Finnigan (1994), Smith and Mullins ological applications, in order to make information (2001), Strangeways (2003) and WMO (1984, 1994b, available to assist farmers all the time at the field 2008a, 2008b). In relation to operational agromete- level, to prepare advisories, and to allow for orology, reference can be made to certain chapters longer-term planning, it is necessary to combine in Rosenberg et al. (1983), Griffiths (1994), Baldy the agricultural and the meteorological data. To and Stigter (1997), and WMO (2001b). make better use of the agrometeorological data in supporting agrometeorological services and to The observations required depend on the purpose provide for effective transfer of the knowledge of for which they will be used. For the characterization agrometeorology to farmers at farm level, the of agroclimate, for climate monitoring and science of information technology is also very prediction, and for the management of natural useful (see also Chapter 17 of this Guide). resources, national coverage over periods of many years is required. These data also provide the 2.1.2 Physical climatic variables background for the shorter-term decision-making involved in activities such as response farming, Agricultural meteorology is concerned with every monitoring of, and preparedness and early warning aspect of local and regional climates and the causes for, natural disasters, along with forecasts for pests of their variations, which makes standard and diseases. For these activities, additional observation of climatic variables a fundamental 2–2 GUIDE TO AGRICULTURAL METEOROLOGICAL PRACTICES necessity (for instance, Hubbard, 1994). It is also accuracy. Biological observations generally are concerned with any climatic modifications, which phenological or phenometric in nature or both. may be introduced by human management of Phenological observations are made to evaluate agriculture, animal husbandry or forestry operations possible relations between the physical environ- (for example, Stigter, 1994a). Physical variables of ment and the development of plants and animals, climate are observed to assist the management of while the phenometric types are made to relate the agricultural activities. Such management includes physical environment with biomass changes. The determining the time, extent and manner of Manual on the Global Observing System (WMO-No. cultivation and other agricultural operations 544) and some of the WMO Technical Notes1 (sowing; harvesting; planting; application of include certain details about observations of this biocides and herbicides; ploughing; harrowing; type. Literature covering this topic is given in 2.3.2 rolling; irrigation; suppression of evaporation; and biological measurements are provided in 2.4.2. design, construction and repair of buildings for Important observations include assessments of storage, animal husbandry, and so on) and different damage caused by weather, diseases and parasites, methods of conservation, industrial use and as well as measurements of growth and yield. transport of agricultural products. 2.1.4 Scale of observations Indispensable climatic parameters in the develop- ment of agricultural meteorology include, more or In agricultural meteorology, observations are less, all those pertaining to geographical climatol- required on the macro-, meso- and microscales. On ogy, especially those that allow interpretation of the larger scales it should make use of all available physical processes in the lowest atmosphere and local observations of environmental physical upper soil layers, which are the climatic determi- parameters made by the international synoptic nants for the local or regional biosphere (Monteith network of stations (see also 2.1.5). In practice, and Unsworth, 2007). Parameters pertaining to observations can be used in real time in agriculture. energy and water balance are thus very important, For parameters with very little spatial variation such as precipitation, humidity, temperature, solar (such as sunshine duration), low-density observa- radiation and air motion. Further, certain physical tion networks normally suffice for agricultural and chemical characteristics of the atmosphere, purposes. Most of the planning activities in the precipitation and soil are also important in agricul- agricultural realm, however, require higher-density tural meteorology. These characteristics can include data. These can sometimes be obtained from synop- CO2 and SO2; dissolved and suspended matter in tic station observations through the use of precipitation; and soil temperature, moisture and appropriate interpolations (Wieringa, 1998; WMO, salinity. Such measurements require specialized 2001b). For biometeorological research, microscale equipment, which is available only at a few selected observations are often required. stations. Non-routine physical (and biological, see below) observations, such as those required for New typical characteristic distances of these climatic research, surveys and special services (as discussed scales are referred to in Chapter 1 of WMO (2008b). in Baldy and Stigter, 1997, for example, and In this publication the mesoscale is defined as 3 km Appendix II to this Guide), are usually more detailed to 100 km, the toposcale or local scale as 100 m to than standard observations and thus need to be 3 km and the microscale as less than 100 m (in the more accurate whenever processes must be studied last case with the notation “for agricultural meteo- instead of phenomena. rology”). Indeed, a mesoscale of 100 km does not feel right in agricultural production and toposcale is also not the right term for a farm. In WMO 2.1.3 Biological variables (2008b), however, it is also stated in particular that Besides scientific observation of the physical envi- applications have their own preferred time and ronment, the simultaneous evaluation of its effect space scales for averaging, station density and reso- on the objects of agriculture, namely, plants, lution of phenomena: small for agricultural animals and trees, both individually and as commu- meteorology and large for global long-range fore- nities, is also a prerequisite of agricultural casting. With respect to agricultural meteorology meteorology. The routine observations provided by climatological and agrometeorological stations should be accompanied by routine biological obser- 1 Please note that the following WMO Technical Notes are vations. In order to obtain the best results, these listed for further reading on subjects